The present invention relates to a semiconductor device and a manufacturing method thereof.
At present, MOS (Metal Oxide Semiconductor) transistors for logic circuits used for LSI (Large Scale Integration) products in general at a technology node of 28 nm to 22 nm are mass-produced as advanced devices. At a technology node of 100 nm or less, the line width of becomes equal to the grain size of a polysilicon electrode used as a gate electrode. The adverse effects on microprocessing techniques, such as deterioration in the lithography precision due to the plane roughness caused by a grain, and a line edge roughness obtained after dry etching, are no longer negligible.
Japanese Unexamined Patent Application Publication Nos. 2006-120734 and 2001-210593 disclose a method of manufacturing a semiconductor device including polysilicon films. Japanese Unexamined Patent Application Publication Nos. 2006-120734 and 2001-210593 disclose a method for forming polysilicon films in a plurality of installments. According to the manufacturing method disclosed in Japanese Unexamined Patent Application Publication No. 2006-120734, a gas containing oxygen is supplied during the period between the step of forming a first polysilicon film and the step of forming a second polysilicon film. By bringing oxygen into contact with the first polysilicon film, the crystal growth of the polysilicon film is stopped. As the gas containing oxygen, an O2 gas, an NO2 gas, or an NO gas is used.